1. Field of the Invention
The present invention relates to an optical coherence tomography apparatus, a method of controlling the optical coherence tomography apparatus, a storage medium, and an ophthalmic system.
2. Description of the Related Art
Currently, various types of ophthalmic apparatuses using optical apparatuses are used. For example, various types of apparatuses, such as an anterior ocular segment imaging apparatus, a fundus camera, and a scanning laser ophthalmoscope (SLO), are used as optical apparatuses for observing the eyes. Of these apparatuses, an optical coherence tomography apparatus based on optical coherence tomography (OCT) using multiwavelength interference is an apparatus capable of obtaining a tomogram of the eye to be examined with a high resolution. This apparatus will be referred to as an OCT apparatus hereinafter. The OCT apparatus has currently been becoming an indispensable apparatus as an ophthalmic apparatus for out-patient clinics dedicated to retinal diseases.
An OCT apparatus is an apparatus which irradiates a sample with measurement light, which is low-coherent light, and can measure backscattered light from the sample with high sensitivity by using a coherence system. The OCT apparatus can capture a tomogram of the retina of the eye to be examined with a high resolution, and hence is widely used for ophthalmic diagnosis and the like of the retinas. In addition, the OCT apparatus is widely used for progress observation to precisely check the patient's progress after an operation or to precisely check the advancement of eye disease.
In order to perform progress observation using such an OCT apparatus, it is necessary to compare tomograms of the same region in the eye to be examined in the X and Y directions. For example, Japanese Patent Laid-Open No. 2008-5987 discloses a technique of storing the scanning position of a tomogram captured in the past, and reproducing the scanning position in the X and Y directions at the next imaging time to perform imaging. This technique is configured to use, as information indicating a scanning position, driving information of a galvano mirror for scanning measurement light (for example, the reflection angle, operation pattern, and the like of the mirror) and reproduce the same driving information at the next imaging time.
Japanese Patent Laid-Open No. 2010-110391 discloses a technique of storing a scanning position at which a tomogram was captured in the past, in association with a fundus observation image at the time of tomography to compare tomograms of the same region of the eye to be examined in the X and Y directions. This technique is configured to compare a past fundus observation image with a current fundus observation image and correct the scanning position of a tomogram to be currently captured in the X and Y directions based on the positional shift amount between the tomograms.
In order to observe the progress of the eye to be examined using the OCT apparatus, it is important to not only image the same region in the X and Y directions but also to perform matching of the coherence gate (a position corresponding to a reference optical-path length in a measurement optical path), the slant, the brightness, and the like between tomograms to be compared. If, however, layer thicknesses are measured, for example, without achieving matching in the slant between tomograms to be compared, different distances are obtained with respect to the same layer because layer thicknesses are generally measured in the Z direction of tomograms. This poses a problem in terms of measurement accuracy. In addition, if layer detection is performed without achieving matching in brightness between tomograms, for example, a layer detected in a past tomogram may be not detected in a current tomogram. This poses a problem in terms of measurement accuracy.